My front seats have a really basic system - originally a couple of chunks or wood with a semicircle routed down the centre which the seat tubes slide forward and back in. They were held in place with a chunk of flat metal bar which tightened with a bolt/wing nut fastened through the floor.
As are mine, with loose pads sitting on the springs. The first owner visited a couple of weekends ago. He assured me that the seats were as he bought it, and they took the pads out to use in the tent when they went camping. Nothing smart in those days!
